Arrangement for modulation



Jan., 24, i939. w. HHNLE 2'449655 ARRANGEMENT FOR MODULATION F1166. Feb. 5, 1957'- Patented Jan. 24, 1939 UNITED STATES PATENT OFFICE ARRANGEMENT FOR MODULATION Germany Application February 3, 1937, Serial No. 123,769 In Germany February 5, 1936 4 Claims.

In the modern art of carrier frequency the development of simple modulating arrangements suiicing the most stringent requirements assumes a prominent place. The prior art has disclosed a number of modulation arrangements using oxide type rectiers or tubes and it has been observed that twin push-pull modulators are particularly suitable for elimination of undesirable modulation products. Thus the prior 0 art has for instance disclosed a double push-pull modulator using oxide rectifiers whereby the four rectifier arrangements form a closed train (ring modulator).

'Ihe present invention concerns an improvement in twin push-pull modulators and suiiices a number of demands that the prior art has so far been unable to realize. Thus for instance, among others, the possibility is given by the suitable choice of rectier characteristics to remove undesirable side bands, that up to the present did not lend themselves to shielding measures and which are produced by modulation of higher order, for instance, fh-l-Zfn, fh-i-Bfn etc., Where fh is the carrier frequency, fn the signal frequency.

In accordance With the invention a modulation arrangement is developed using a twinpush-pull arrangement of the non-linear resistances in the manner that they are disposed in form of a star. In other words, all poles of the same sign of the non-linear resistances are onesidedly connected in one point.

In describing my modulation means more in detail reference will be made to the attached drawing wherein Figures 1 to 3 inclusive each shows a twin push pull modulation system arranged in accordance with my invention. In Figures 1 and 2 two electrode rectiers of different type are used, while in Figure 3 electron discharge rectiers of the control grid type are used. Figure 4 shows schematically a tube structure wherein the several electrode systems of an arrangement as shown in Figure 3 are included in a single closure member. Figure l shows a star-like arrangement of four oxide rectier elements G11-G4. All these oxide rectifers are connected with their side of equal sign to common point S, the star point. The frequencies to be modulated are taken from generators and 2 and brought to the modulating arrangement through transformers U1 and U2 while the modulation products are tapped at resistance 3 representing any utilization circuit. To simplify the drawing the winding of the various transformers have been disassociated. However, the

several windings of each transformer are designated by a common symbol.

In this embodiment the leads for the potentials are selected symmetrically resulting in a decoupling with respect to the other frequency at a given moment. The two lead windings of transformer U1 are provided with center taps connected to star point S and in whose line train are connected, symmetrically to star point S, the transformer windings of U2. The combination of both branches is eifected at point S1 which may coincide with the star point or, as in Figure 1, offers the possibility to interconnect a biasing potential current source, for instance battery B. This symmetrical arrangement fur-` ther has the advantage that energy source I and 2 may be exchanged, insuring the optional choice to feed the carrier frequency to I and the signal frequency to 2 or vice versa. The

modulated frequency is delivered at the four` transformer windings of U3.

The introduction of biasing potential source B in the circuit arrangement according to invention offers further advantages which shall be discussed in more detail in what follows: It is known in the prior art that by impressing a biasing potential in the case of non-linear resistances the working point may be moved in its location. Several advantages may be obtained in this manner with respect to the modulation, but in the circuit arrangements known in the prior art the impression of a biasing potential encountered practical dificulties since the use of a single joint battery was excluded. What actually would have to be done is to provide each branch of the twin push-pull arrangement with a special biasing potential source which besides would be impressed with different alternating current potential. The present invention eliminates this diiiiculty.

Moreover, the use of oxide type rectiers 'in these arrangements has proved quite troublesome in that the influence of the capacity is very great in carrier currents of higher frequency, thus limiting greatly the use of these modulation arrangements for higher frequencies. The use of a biasing potential battery insures the reduction of the detrimental iniiuence of the capacity of the rectiers. In addition, the biasing potential may further be used for regulating the wave t resistance of the modulator which may for instance be of great importance in carrier cu'rrent systems over cables. The biasing potential battery may further be used to particular 'advantage for starting and stopping operations,-

The invention is not restricted to the use of oxide rectiers as non-linear resistances but all arrangements with curved characteristics may be employed. Thus, use may be made for instance of selenium rectiers, glow tubes, or valves, and the choice of either diodes or grid-controlled tubes is immaterial.

Figure 2 shows the same circuit arrangement as Figure 1, using four diode paths D1-D4 in place of the rectifiers. Also in this case a biasing potential battery is arranged in connection with the star point. Figure 3 illustrates an embodiment of a circuit arrangement with gridcontrolled tube. Tubes R1--R4 are interconnected in a manner similar to the arrangement shown in Figure l with rectiers with the difference that the windings of transformer U2, coupled with generator 2, are connected to the grids of the Atubes while the mid-points of the transformer windings of U1 are in direct connection and are impressed with anode battery potential AB with respect to cathode potential. A grid biasing potential battery GB is likewise provided.

These examples plainly show the considerable simplifications resulting from the circuit arrangement acoording to invention since only one grid and one anode potential source is required for all the tubes. It may prove suitable in many cases to equip modulators with grid-controlled tubes for the use of higher power is insured thereby. With higher powers however, the demands for an exactly symmetrical structure are no longer so stringent. The allowable asymmetry of the elements is given by the required proportion carrier quiescent current to modulated current (useful current). With given asymmetry, this ratio depends on the ratio carrier current to useful current. The useful current is proportional to the fed eurent to be modulated. Consequently, the radio of fed current to carrier current is decisive. This ratio may increase with suitable characteristic of tubes and suitable form of curve. But even in other respects the tube modulators may result in special advantages.

As observed previously, the present invention insures the reduction of the undesired side-bands Afh-l-Zfn, fh-i-3fn, etc. This may be accomplished in various manners, thus by reduced modulation so that the resistance of rectifier is a linear function of the current. Another alternative however, consists in modulating strongly with a carrier frequency of rectangular form for which the tube modulators are especially suitable. When tubes are used their internal resistance may easily be varied between limits as low as 5,000 ohms, on the one hand, and practically iniinity, say 50,000,000 ohms, on the other hand, so that the ratio of these resistances may readily be made as high as say 10,000 for example. f the terminal resistance is chosen in usual manner equal to the geometric average, the small variations of blocking and transmission resistance, due to other currents, are of no importance. Hence, the side-bands fh-i-Zfn and so forth are greatly reduced.

The use of grid-controlled tubes is not restricted to high-vacuum tubes. It is possible to employ in their place grid-controlled gas or vapor discharge paths. The latter are particularly adapted for use with low frequencies since its transmission resistance is smaller than that of vacuum tubes. Use for instance may be made of under-heated tungsten tubes in order to obtain a nearly rectangular carrier current, the tubes being modulated from the lower bend through to the saturation current. By this means a good approximation to rectangular form may be obtained since a limit is set merely by the self-capacities of the elements.

Since, as described above, only one joint grid and anode battery is used for the four tubes, a constructive simplification may be accomplished in accordance with further invention and all tube systems may be disposed in a joint vessel. But since all cathodes are connected to the star point it is further feasible to construct a multiple system with joint cathode. An embodiment of a tube of this type is shown in Figure 4. Around cathode K are arranged concentrically the four grids G and four anodes A in the form of a circular arc. It appears necessary, for electric separation of the individual systems, to insert shields and thus four shields S are inserted between the individual partial systems as shown in this embodiment, representing for instance space charge grids. But the structural development of tubes of this type is not restricted to the arrangement indicated in the iigure.

It may finally be remarked that the star modulation arrangement according to invention may be equipped with more than one rectifier element per branch and may be imparted for special purposes the form of a double bridge. The arrangement may be directly used in reverse sense as demodulator.

I claim:

l. In a modulation system, a plurality of pairs of rectiiiers each having like electrodes including a cathode, a connection between the cathodes of all of said rectiers, a source of wave energy, symmetrical means for impressing wave energy from said source in phase opposition between corresponding electrodes in each pair of said pairs of rectiers, a second source of wave energy, symmetrical circuit means for impressing wave energy from said second source in phase to corresponding electrodes in each pair of said pairs of rectifers, a source of direct current potential connected at one terminal to said cathodes and at the other terminal to said last named circuit means for impressing operating potentials between each of said cathodes and said last named corresponding electrodes, and a load circuit coupled to corresponding electrodes in each of said rectiers.

2. In a modulation system, a plurality of pairs of electron discharge devices each having an anode, a cathode, and a control grid, means tying the cathodes of said discharge devices together,

a source of wave energy of a first frequency, a

source of wave energy of a second frequency, symmetrical circuits for impressing energy from said source of energy of said first frequency in phase opposition between the anode electrodes in each pair of said pairs of said electron discharge devices, a source of direct current potential connecting a point of symmetry on said last named means to the cathodes of said tubes, symmetrical means for impressing wave energy from said source of wave energy of said second frequency in phase on the control grid electrodes in each pair of said pairs of electron discharge devices, a source of potential connecting a point of symmetry on said last named means to the cathodes of said tubes, and a load circuit symmetrically coupled to the anodes of each pair of said pairs of tubes.

3. A system as recited in claim 1 wherein a second source of potential has its positive terminal connected to a point of symmetry on said first named symmetrical means and its negative terminal connected to the cathodes of said tubes.

4. In a modulation system, a plurality of pairs of diode rectiers each having an anode and a cathode, means connecting the cathodes of said diode rectiers together, a source of wave energy of a rst frequency, a source of wave energy of second frequency, symmetrical transformer means connecting said source of wave energy of said rst frequency in phase opposition between the anodes of each pair of said diode rectifiers, said connections each including a secondary winding of a transformer having a primary winding coupled to said source of wavev energy of said second frequency, a load circuit comprising a transformer having primary windings included in each of said last named couplings, and a secondary winding connected with a load, transformer means for impressing wave energy from said source of wave energy of said rst frequency on the anodes of said rectifier, said transformer means comprising secondary windings connected between points of symmetry on said first named secondary windings and coupled to a primary winding connected with said source of wave energy of said first frequency, and a source of potential connecting the cathodes of said tubes to a point of symmetry on said last named circuit.

WALTER 

